Internal tube peltier cooling of image intensification photocathodes

ABSTRACT

An intratube Peltier cooling device for cooling a photoemissive device mounted in a sealed housing of an image intensifier device. The cooler consists of at least a pair of N and P type material semiconductor elements having a centrally located cold junction element which surrounds the periphery of the photoemissive device. A hot junction is positioned adjacent the outer periphery of the semiconductor elements and extends through the sealed tube walls of the image intensifier device. Electrical connection is provided at the external periphery of the hot junction.

United States Patent Wilson et al. 1 Aug. 7, 1973 [54] INTERNAL TUBE PELTIER COOLING OF 3,316,474 4/1967 Lode 136/204 X IMAGE INTENSIFICATON 3,273,347 9/1966 Elfving 136/204 X PHOTOCATHODES 3,635,037 1/1972 Hubert 136/204 X I [75] lnventorsz' Herbert L. Wilson, Woodbridge',

Hans D. Pommerrenig, Springfield; Primary Examiner-Roy Lake- William A. Gutierrez, Woodbridge, qsi gmtli gy ng ggh D- a r all of Va." Attorney-Harry hf Saragovitz, Edward J. Kelly [73] Assignee: The United States of America as et represented by the Secretary 01 the Army, Washington, DC. ABSTRACT [22] Filed: 1"- 1972 An intratube Peltier cooling device for cooling a photo- [21] Appl' N05 247,313 emissive device mounted in a sealed housing of an image intensifier device. The cooler consists of at least v a pair of N and P type material semiconductor elements [52] US. Cl SIS/50,625, 136/204, h i a centrally located ld junction element which 1 1 12 surrounds the periphery of the photoemissive device. A [51 I Int. Cl. H01] 7/44 junction is positionedadjacent the Omar periphery [581 Field of Search 315/50, 1 12; 313/94, of the semiconductor elements extends through the l 1; 136/203 204; 62/3 sealed tube walls of the image intensifier device. Electrical connection is provided at the external periphery [56] References Cited f h hot junction.

' UNITED STATES PATENTS 7 Claims, 6 Drawing Figures 3,515,924 6/1970 'Moegenbier 313/94 PAIEIIIEII M19 7 I973 SIIEEIEIIFQ FIG. 4

T N E R R U C N m TS MP m w98765432 l O O 6 H Y R m S w H E m T w m0 MM 0 .0 C W 2 E l mm mm .0 A T C O H 0 5 505000 0 223 4 80v msmk 29:022 0400 TIME (SEC-I CATHODE COOLING TIME HISTORY S P M A w9876543 l HOT JUNCTION CURRENT HOT JUNCTION 23 C FIG. 5

3'0 TIME (SEC) CATHODE COOLING TIME HISTORY FIG. 6

HOT JUNCTION +20 HOT JUNCTION CURRENT TIME ISEC.)

v mEmF 20:022 0400 BACKGROUND The present invention relates to the intratube cooling of an internally mounted photoemissive device of an image intensifier device.

Prior image intensifiers utilized a cathode coating on a face of the image intensifier device. Cooling of the device was achieved by surrounding the device with cooling structure that was in heat conducting contact with its housing. If the photocathode was separately internally mounted within the tube, additionally, an airtight housing around the tube window was required to prevent window fogging.

SUMMARY The advantages of the instant solution to this problem, in addition to many other benefits, arem ade evident from the following summary:

1. direct cooling of thephotoemissive device produces faster tube response;

2. extremely light weight-less than 1% of the weight of an external cooler;

3. low power requirement-less than 10% of the power required by an external cooler;

4. no air-tight housing is required around the tube window;

5. smaller heat sink required only 10% of that re-' quired by external cooler;

' 6. possible to use thin film cooling elements produced, for example, by epitaxial growth, sputtering or evaporation;

7. by reversal of potential to the cooler's electrodes, the cathode may be heated for activation, cleaning or outgassing or other particular tube operation.

It is, therefore, the purpose of this invention to provide a cooling arrangement for an internally mounted photoemissive device which will be extremely light in weight and require dramatically reduced power requirements over that of any known external cooler arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a longitudinal cross-section of an image intensifier tubeincorporating the intra-tube Peltier cooling means,

FIG. 2 is a view of a modified photoemissive device- Peltier cooler combination in the image intensifier housing, 7

FIG. 3 is a Peltier cooler arrangement having a plural module, multiple stage configuration,

FIGS. 4, 5 and 6 show typical test results for the disclosed Peltier cooler of single stage configuration.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference characters correspond to like elements in the following description, there can be seen in FIG. 1 an image intensifier 11 having a sealed housing 12. An optical window 13 receives input radiation that is to be transmitted through housing 12 for impingement upon a photoemissive device l5.' The photoemissive device 15 functions as a two-dimensional space current amplifier coupled to an output means 14 which may take the form of an electron coupler or, as specifically shown in FIG. 1, a phosphor coated element '16. Internally mountedand contacting the photoemissive element 15 can be seen the Peltier cooling apparatus. In this embodiment, the Peltier cooling apparatus comprises a cold junction element 17 disc-like in shape, and having a central aperture. The surface of the disc-like element is placed in face-to-face contact with the photoemissive element 15. P and N type semiconductor elements of the Peltier cooler are in the form of concentrically arranged, mutually insulated cylinders 18 and 19. One end of each of the two cylinders contacts the face of the disc-like cold junction 17 opposite that face of the cold junction that is in contact with the photoemissive element 15. The hot junction of the Peltier cooling device comprises a pair of conducting elements 20 and 21 in contact with the semi-conductor cylinders 18 and 19 respectively. These hot junction elements 20 and 21 penetrate the housing 12 and form the requisite power terminal for the Peltier cooler.

Turningnow to the modified cooler arrangement in FIG. 2, we find in the Peltier cooling device, a cold junction contact element 22 which is placed in thermal contact with the circumference of a photoemissive device 23. Surrounding the photoemissive device 23, and in contact with the cold junction 22, are a pair of discs 24 and 25 of semiconductor P-type and N-typ'e materials respectively. These discs as well as the other disclosed semiconductor pairs may be fabricated from such materials as PbTe, -Bi Se Bi Te or Sb Te which have high figures of merit (z). But, should it be necessary to sacrifice these high figure of merit materials for lower figure materials having higher temperature capability, resort may be had to such materials as silicon, germanium, boron-carbon, etc. But, as these lower figure of merit materials result in lower cooling increments, it may be necessary to increase the number of stages necessary to achieve a particular value of net cooling. The semiconductor material discs 24 and 25 areinsulated from each other. This is accomplished, for example, either by spacing them apart or by use of an insulating spacer 26. Contacting the outer perimeter of the discs 24 and 25 is the hot junction of the Peltier cooler formed from electrically and thermally conductive components 27and 28. These components extend through the walls of the sealed housing and provide the Peltier cooler with the necessary electrical power connections as well as a heat sink in the event that the housing 12 is itself not thermally conductive.

Should it be necessary to achieve a greater degree of cooling than can be accomplished with a single stage cooler, an internal Peltier cooler can be fabricated uti-' lizing a multi-stage arrangement in which an array of multistage modules are placed about the photoemissive device. Each module can be of the well known pyramid design wherein each stage progressing from the apex of extends through the housing wall 12 of the intensifier device. If the housing 12 is made of thermally conductive material, it alone can serve as the heat sink. Electrical contacts 34 are provided to power the Peltier cooler.

FIGS. 4, 5, and 6 represent test results of an internal Peltier cooler of the type shown in FIG. 2. As can be seen from the curves of cold junction temperature versus time, the required cooling time of the cold junction for the hot junction temperature maintained variously at 40, 23 and 2 Centigrade, drops increasingly rapidly as the current supplied to the hot junction terminals is increased; the cooling times being reckoned in seconds. The required cooling time for the disclosed device is therefore a small fraction of the cooling time of any known external cooler for a similar device.

Obviously, the invention may be practiced with numerous other- Peltier cooler arrangements mounted within the sealed housing of the image intensifier described. Therefore, it is understood that various changes, modifications and alterations may be accomplished within the scope of the invention as defined by the following claims.

We claim:

1. A sealed internally cooled image intensifier device comprising:

a sealed housing having an optical window;

photoemissive means positioned within said housing;

intratube Peltier effect cooling means associated with said photoemissive means for direct cooling thereof; and

optical output means in optical alignment with said window and said photoemissive means.

2. An image intensifier device as in claim 1 wherein said Peltier effect cooling means comprises:

a cold junction element in thermal contact with said photoemissive means;

at least a pair of P and N type semiconductor elements i contact with said cold junction; and,

hot junction means comprising a pair of thermally and electrically conductive elements each respectively contacting one of said semiconductor elements and passing through said sealed housing,

25 photoemissive means mounted in said housing in optical alignment with said optical window and said optical output means;

Peltier cooling means in heat conducting contact with said photoemissive means, said cooling means comprising conductive cold junction means peripherally contacting said photoemissive means;

at least a pair of mutually insulated members of P- type and N-type semiconductor materials respectively in conducting contact with said cold junction means; and,

hot junction conductive means in contact with the outer periphery of said semiconductor members and extending through said sealed housing, thereby providing electrical and thermal feed thru to produce the Peltier cooling effect at said photoemissive means when connected to an electrical source.

1 t i i thereby providing external electrical contacts for the Peltier effect cooling device. 3. The device as in claim 2 wherein said semiconductor elements are disc-shaped and have a central aper- 5 ture peripherally contacting the cold junction element.

4. The device as in claim 2 wherein: said cold junction element comprises an apertured disc in face contact with said photoemissive means; and, said semiconductor elements comprise a pair of concentric cylinders each having a base in contact with a face of said cold junction element.

5. The device as in claim 2 wherein plural Peltier cooling modules are arrayed about and in contact with said cold junction.

6. The device as in claim 5 where said plural cooling modules each comprise multiple stages; the hot junction of each stage being cooled by the cold junction of the next suceeding stage.

7. An image intensifier tube containing an internally cooled photoemissive means and comprising:

a sealed housing having an optical window at one end of said housing and an optical output means at the opposite end thereof;

LII 

1. A sealed internally cooled image intensifier device comprising: a sealed housing having an optical window; photoemissive means positioned within said housing; intratube Peltier effect cooling means associated with said photoemissive means for direct cooling thereof; and optical output means in optical alignment with said window and said photoemissive means.
 2. An image intensifier device as in claim 1 wherein said Peltier effect cooling means comprises: a cold junction element in thermal contact with said photoemissive means; at least a pair of P and N type semiconductor elements in contact with said cold junction; and, hot junction means comprising a pair of thermally and electrically conductive elements each respectively contacting one of said semiconductor elements and passing through said sealed housing, thereby providing external electrical contacts for the Peltier effect cooling device.
 3. The device as in claim 2 wherein said semiconductor elements are disc-shaped and have a central aperture peripherally contacting the cold junction element.
 4. The device as in claim 2 wherein: said cold junction element comprises an apertured disc in face contact with said photoemissive means; and, said semiconductor elements comprise a pair of concentric cylinders each having a base in contact with a face of said cold junction element.
 5. The device as in claim 2 wherein plural Peltier cooling modules are arrayed about and in contact with said cold junction.
 6. The device as in claim 5 where said plural cooling modules each comprise multiple stages; the hot junction of each stage being cooled by the cold junction of the next suceeding stage.
 7. An image intensifier tube containing an internally cooled photoemissive means and comprising: a sealed housing having an optical window at one end of said housing and an optical output means at the opposite end thereof; photoemissive means mounted in said housing in optical alignment with said optical window and said optical output means; Peltier cooling means in heat conducting contact with said photoemissive means, said cooling means comprising conductive cold junction means peripherally contacting said photoemissive means; at least a pair of mutually insulated members of P-type and N-type semiconductor materials respectively in conducting contact with said cold junction means; and, hot junction conductive means in contact with the outer periphery of said semiconductor members and extending through said sealed housing, thereby providing electrical and thermal feed thru to produce the Peltier cooling effect at said photoemissive means when connected to an electrical source. 